1. Field of the Invention
The present invention relates to a dielectric resonator, a dielectric filter, a dielectric duplexer, and a communication device each for use in a communication base station, and a method of producing a dielectric resonator.
2. Description of the Related Art
Such dielectric resonator and dielectric filter will be described with reference to FIGS. 12 through 14. FIG. 12 is a perspective view of the dielectric resonator. FIG. 13 is a partly cross sectional view of one end of the dielectric resonator. FIG. 14 is an exploded perspective view of the dielectric filter. In this case, the filter will be described by use of a two stage band-elimination dielectric filter in which two dielectrics are connected with a quarter-wave line. This filter was not a publicly known conventional technique when Japanese Patent Application No. 10-118933, which is a basis of claim of priority for the application of the present invention, was filed.
As shown in FIGS. 12 and 13, a dielectric resonator 110 is composed of a columnar dielectric 111, and thin film multi-layers 112 formed on the opposite sides of the dielectric 111. In the case that the thin film multi-layer electrodes 112 are employed as the electrodes of the dielectric resonator 110, the nonloaded Q of the dielectric resonator 110 is enhanced. As compared with monolayer silver electrodes used as the electrodes, the dielectric resonator with high characteristics can be provided.
In addition, as shown in FIG. 14, a dielectric filter 120 is made up of a shield cavity 121 made of iron or the like, two dielectric resonators 110 arranged in the shield cavity 121, and a ground plate 122, electrical probes 123 as external coupling means, and external connectors 124 attached to the shield cavity 121.
As described above, each dielectric resonator 110 is formed of the columnar dielectric 111 having the thin film multi-layer electrodes 112 formed on the opposite sides thereof. One electrode surface of the dielectric resonator 110 is soldered to the ground plate 122 having a step 122a and a hole 122b for soldering. The ground plate 122 is sandwiched between the body 121a of the shield cavity 121 and a lid 121b. Thus, the dielectric resonator 110 is arranged in the shield cavity 121. In addition, the electrical probes 123 are connected at one end to the center conductors of the external connectors 124, respectively, and are elongated in the spaces between the dielectric resonators 110 and the shield cavity 121. Moreover, the center conductors of the two external connectors 124 are connected through a quarter-wave line 125.
In the dielectric filter 120 having the above-described configuration, an input signal, when it is input through the external connectors 124, is transmitted to the electrical probes 123, so that the electrical probes 123 and the dielectric resonators 110 are capacitively coupled. Then, the dielectric resonators 110 resonate at a resonant frequency determined by the shapes and sizes of the dielectric resonators 110. Thus, the dielectric filter 120 in which the dielectric resonators are connected through the quarter-wave line 125 for connection is provided functions as a band-elimination dielectric filter for eliminating the desired frequency.
In general, a great number of dielectric resonators having a predetermined diameter and thickness are produced at one time. Accordingly, in order to allow the dielectric resonators to be used in dielectric filters of which the frequency characteristics are different, it is necessary to adjust the resonant frequencies of the dielectric resonators in correspondence to the frequencies. To make this adjustment, in the above-described dielectric resonator, it is possible to cut either the peripheral side-face of the dielectric resonator having thin film multi-layer electrodes formed on the opposite sides thereof, including the thin film multi-layer electrodes, to partially cut or the thin film multi-layer electrodes.
However, as shown in FIG. 15, if the adjustment of the resonant frequency is carried out by the above-described method, for example by cutting, the peripheral side-face of the dielectric 111, in the thin film multi-layer electrode 112 comprising metallic layers 112a made of copper or the like and dielectric layers 112b, due to the rolling properties of the metallic layers 112a, a part of the metallic layers 112a of the thin film multi-layer electrode 112 will be short circuited, so that the nonloaded Q of the dielectric resonator 110 will be reduced. Therefore, after the peripheral side-face is cut to adjust the resonant frequency of the dielectric resonator, etching or the like is required to remove the short circuiting portion of the thin film multi-layer electrode. Thus, the number of production processes is increased.
Further, to adjust the resonant frequency of the dielectric resonator, a method of cutting the dielectric portion of the dielectric resonator excluding the thin film multi-layer electrode may be proposed. However, to adjust roughly the resonant frequency, it is required to cut an amount of the dielectric. When the dielectric of the dielectric resonator is partially removed, the symmetric structure of the dielectric resonator is unbalanced, so that the current distribution becomes uneven, and the nonloaded Q of the dielectric resonator is reduced.